def compare(node_value, target):
    if node_value > target:
        return -1
    elif node_value < target:
        return 1
    else:
        return 0


def validateBst(node):
    # Write your code here.
    if (node.left is None or node.value > node.left.value) and (node.right is None or node.value <= node.right.value):
        return validateBst()